Immunotherapy involves evoking an immune response against cancer cells based on their production of target antigens. Immunotherapy based on cell-mediated immune responses involves generating a cell-mediated response to cells that produce particular antigenic determinants, while immunotherapy based on humoral immune responses involves generating specific antibodies to cells that produce particular antigenic determinants.
Recent studies show that immunotherapy of cancer patients may be dramatically improved by the finding that CD8+ CTL recognize and kill tumor cells that display peptides from tumor-associated antigens within MHC Class I molecules. For example, in clinical studies it has been found that effector CD8+ T cells play a major role in tumor regression. Several tumor antigens in prostate cancer models have been identified and HLA allele-specific peptides from those prostate cancer-associated antigens have been identified as CD8+ T cell epitopes. For example, HLA-A2.1 binding peptides were described that were derived from prostate specific antigen (PSA) (Correale et al., J Immunol 161:3186, 1998), prostate-specific membrane antigen (PSMA) (Tjoa et al., Prostate 28:65, 1996), prostate stem cell antigen (PSCA) (Kiessling et al., Int J Cancer 102:390, 2002), and prostate acid phosphatase (Peshwa et al., Prostate 36:129, 1998). For PSA, clinical trials are in progress using different vaccine strategies.
However, there clearly is a need to identify additional antigens for use as therapeutic agents to treat other types of cancer.